1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to a rotary force controlling apparatus of an image forming apparatus that controls a rotary force transferred to a rotary body mounted on a shaft.
2. Description of the Related Art
Generally, an image forming apparatus, such as a laser printer, an LED printer, a digital copier, or a facsimile machine, transfers an image signal according to a digital signal input from a computer or a scanner onto a recording medium in a visible image form. This image forming apparatus includes an image forming unit for forming an image on a sheet, and a feed device for feeding the sheet to the image forming unit. The feed device and other devices used in the image forming apparatus use a rotary force controlling apparatus for controlling a rotary force transferred to a rotary body that is mounted on a rotary shaft. A conventional rotary force controlling apparatus used in a feed device of an image forming apparatus is described as an example.
FIG. 1 is a perspective view of a feed device of an image forming apparatus using a conventional rotary force controlling apparatus. FIG. 2 is an elevational view of the conventional rotary force controlling apparatus of FIG. 1. FIG. 3 illustrates the operation of the conventional rotary force controlling apparatus.
Referring to FIG. 1, a conventional feed device 1 includes a driving shaft 3 that is rotated by a driving source (not shown), such as a motor. A roller device 20 includes a driving roller 2 connected to and rotated by the driving shaft 3 and a driven roller 5 tightly attached to and rotated by the driving roller 2. The driven roller 5 is pivoted on levers 10b around a hinge shaft 7 to press against the driving roller 2 under the force of a pressing spring 8. The levers 10b are coupled to and rotate on the hinge shaft 7. One of the levers 10b has a mechanical interrupter 10a that follows a rotary cam 12. The feed device 1 includes the rotary cam 12 to actuate the interrupter 10a and to retract the driven roller 5 from the driving roller 2. When necessary, the rotary cam 12 acts as a clutch 14 for rotating the rotary cam 12.
When the driving roller 2 of the feed device 1 rotates, the driven roller 5 rotates and a sheet passes between the driving roller 2 and the driven roller 5 to an image forming unit (not shown) to form an image on the sheet. The roller device 20 has a pressure for conveying the sheet. Accordingly, when the rear end of the sheet leaves the roller device 20, a sudden impact is applied to the sheet that may distort the image. To prevent such distortion, when the rear end of the sheet leaves the roller device 20, the rotary cam 12 rotates to press the interrupter 10a and to separate the driven roller 5 from the driving roller 2.
The conventional feed device 1 includes a rotary force controlling apparatus 30 having the rotary cam 12 and the clutch 14 to separate the driving roller 2 and the driven roller 5.
Referring to FIGS. 2 and 3, the conventional rotary force controlling apparatus 30 includes a rotary shaft 10, a clutch unit 20 mounted on the rotary shaft 10, and a power transferring member 22 that receives a driving force from a driving source (not shown) to rotate the rotary shaft 10.
A rotary body 12, such as a cam, is mounted on one end of the rotary shaft 10. The clutch unit 20 is mounted around the periphery of the rotary shaft 10 and controls the rotary force transferred from the driving source (not shown) to control the rotation of the rotary shaft 10. The clutch unit 20 includes a clutch 32 mounted around the periphery of the rotary shaft 10 and a rotation controlling unit 50 for controlling the rotation of the rotary shaft 10.
The clutch 32 includes a first positioning unit 33 and a second positioning unit 34 for stopping the rotary body 12 at a predetermined location. The first and second positioning units 33 and 34 protrude from the circumference of the rotary body 12 and are spaced apart from each other.
The rotation controlling unit 50 interferes with the first and second positioning units 33 and 34 to control the rotation of the rotary shaft 10, and includes a bracket 60, an interfering unit 65, and an elastic member 90.
A solenoid unit 70, which is turned on and off by an electrical signal, is mounted on the bracket 60. When the solenoid unit 70 is turned on by the electrical signal, a magnetic force is generated and the interfering unit 65 is attracted to a predetermined location.
One side of interfering unit 65 is mounted on the bracket 60, and the interfering unit 65 interferes with or is released from the first and second positioning units 33 and 34 when the solenoid unit 70 is turned on or off. That is, the interfering unit 65 interferes with the first and second positioning units 33 and 34 mounted on the clutch 32 to control the rotation of the clutch 32. An armature 80 having an engaging unit 82 for interfering with the first and second positioning units 33 and 34 is mounted on one end of the interfering unit 65.
One end of the elastic member 90 is mounted on the bracket 65, and the other end is mounted on the interfering unit 65. The elastic member 90 provides an elastic force to the interfering unit 65 such that the armature 80 is coupled to and released from the first and second positioning units 33 and 34.
By the action of the solenoid unit 70, the armature 80 moves and interferes with the first and second positioning units 33 and 34 to stop the rotation of the rotary body 12 that is mounted on the rotary shaft 10. When the solenoid unit 70 is turned on, the interfering unit 65 moves so that the armature 80 interferes with the first positioning unit 33. When the solenoid unit 70 is turned off, the interfering unit 65 is returned to its original location by the elastic force of the elastic member 90, and is released from the first positioning unit 33 and interferes with the second positioning unit 34. That is, the action of the solenoid unit 70 and the elastic force of the elastic member 90 moves the interfering unit 65 back and forth between the first and second positioning units 33 and 34.
The power transferring member 22 is mounted around the clutch unit 20, and receives the rotary force from the driving source (not shown) to rotate the rotary shaft 10. The power transferring member 22 is preferably a gear. The rotary force transferred by the power transferring member 22 is selectively transferred to the rotary shaft 10 by the clutch unit 20.
The conventional rotary force controlling apparatus 30 includes two positioning units 33 and 34. The locations of the two positioning units 33 and 34 are spaced apart from each other so that the two positioning units 33 and 34 are controlled when the solenoid unit 70 is turned on and off to control the location of the rotary body 12. Accordingly, when the rotary body 12 is continuously held at any one location, the solenoid unit 70 must stay in the ON state or the OFF state.
When the solenoid unit 70 is continuously OFF, there is no problem. However, when the solenoid unit 70 is continuously ON, it continuously draws power and can become overheated. This can weaken its magnetic force and attracting force. Accordingly, the force for attracting the armature 80 is weakened, and thus the armature 80 may not accurately interfere with the two positioning units 33 and 34.
Also, heat generated in the solenoid unit 70 can shorten its life span or damage other components.
Furthermore, when the solenoid unit 70 is in the ON state for a long time, the armature 80 can be magnetized. Thus, when the solenoid unit 70 is turned off, the armature 80 does not immediately separate from the solenoid unit 70. That is, a time delay occurs and the operation of the rotary body 12 cannot accurately be controlled.
Also, since only two positioning units are used, the rotary body 12 cannot stop at three or more locations. Moreover, when the solenoid unit 70 is turned off and then on, the engaging unit 82 of the armature 80 is engaged with the first positioning unit 33 by the time delay. Thus, the rotary body 12 cannot rotate.
Accordingly, a need exists for an improved rotary force controlling apparatus for an image forming apparatus that controls a rotary force transferred to a rotary body mounted on a shaft.